Wildlife Wednesday -- Thatching Ants

By Andy Ames

If you have been out in the meadows and valleys lately you may have noticed an increase in ant activity, particularly the Western Thatching ant. These ants create mounds covered with twigs, or thatch. The nest often starts at the base of a sage brush, wax currant, or similar plant. The ants then chew away the bark and spray formic acid onto the plant until it dies. The plant is then removed allowing a central passage down into the nest. Pretty clever! Thatching ants are omnivores with a diet ranging from other bugs to plant material, carrion and honeydew (a sticky substance created by aphids). An ant colony can be an amazing sight, but be careful, Thatching ants can be defensive around their nest and spray formic acid when threatened or even bite.

Formica obscuripes, or Western Thatching ants, come in a variety of sizes and colors. A single nest colony may have one or several queens, and many thousands of workers.

There are many roles for workers to fill - foraging, maintenance, protection, transporting and caring for the eggs and larvae, and even farming aphids that produce honeydew for food. It is not clear how roles are divided up amongst the workers. Some are likely specialists while others perform numerous tasks.

Thatching ants are diurnal (active during the day). This nest is just waking up for the morning.

Mound glowing red with ant activity.

Ants will use different parts of the thatched mound at various times of day. During warmer periods ants will use entrances shaded from the sun while in the morning and evening, when it is cooler, ants use entrances with more sun exposure.

A very large ant pile under a fallen tree. A single colony may last many years. While most workers live from a few weeks to up to a year, a queen may live a decade or more.